The present invention is a grate clip for use with a stoker grate, for example in a power generator, refuse incinerator or cooling device, and more particularly a slope-sided grate clip having sloping sides so as to shed ash and debris when traveling in an inverted orientation on a return loop of a stoker grate.
Heretofore, a number of patents and publications have disclosed grates and grate clips, the relevant portions of which may be briefly summarized as follows:
U.S. Pat. No. 403,416 to Campbell, issued May 14, 1889, discloses an inclined coal grate. The inclined grate included removable shelves held in place by gravity during reciprocation of adjacent
U.S. Pat. No. 1,339,531 to Wallen, issued May 11, 1920, teaches a mechanical stoker including means to prevent the leakage of air about the ends of grate bars in a traveling grate.
U.S. Pat. No. 1,917,652 to Krieger, issued Jul. 11, 1933, discloses an automatic stoker wherein a traveling grate is employed that uniformly distributes air to the fuel bed, while preventing ash and fuel from sifting through to the air compartment there beneath. The grate clips are affixed to and supported by a series of parallel grate supporting bars, and the fuel is supported on the upper surface of the grate clips.
U.S. Pat. No. 2,955,812 to Boron, issued Oct. 11, 1960 describes a furnace pallet as a replacement to furnace grates that tend to crack, warp and burn out as higher furnace temperatures are used for processing ore.
U.S. Pat. No. 4,200,047 to Knorr, issued Apr. 29, 1980 discloses a two-part grate, having separable front and rear parts, for use in a reciprocating grate system.
U.S. Pat. No. 5,766,001 to Bentson, issued Jun. 16, 1998, describes a grate element formed in the shape of a box and having an L-shaped cross section, wherein the design of the grate element leads a cooling gas through the grate element.
U.S. Pat. No. 5,839,376 to Barlow, issued Nov. 24, 1998, hereby incorporated by reference, teaches a stoker with a universal key construction so as to eliminate the need for distinct overlapping and underlapping keys.
U.S. Pat. No. 5,551,356, for a "TWO PIECE GRATE CLIP FOR USE AS A POWER GENERATOR MAINTENANCE PART," issued Sep. 3, 1996 to Joseph R. Post, is hereby incorporated by reference for its teachings relevant to grate stokers and grate clips.
In "Riley Spreader Stoker Operating Instructions & Parts Catalog" a publication by the Riley Stoker Corporation, Worcester, Mass. (date unknown) pp. 8-10 and Dwg. 5KT-541-3, shows that grate clips traverse a lower return loop of the stoker grate in an inverted position.
Prior art grates, including two part grate clips and also one piece grate clips, are typically connected to the stoker grate with a fastening means such as a bolt or a rigid T-bar support unit. In continuous loop grate systems, the underside of each grate clip is a location where ash, fuel and other debris tends to collect when it falls through the separations between the grate clips. Moreover, low melting point metals (e.g., Al, Pb, etc.), when exposed to the combustion temperatures of a furnace, often melt and drip through the grate clips only to collect on the underside of the return loop of the grate stoker. Build-up of the ash, debris and molten metal deposits requires frequent maintenance or replacement of the grate clips and other stoker hardware. Replacement of the broken or missing grate clips often requires the furnace to be turned off and the stoker to be idled. Because shutting down a furnace is costly, it is desirable to avoid or reduce or eliminate the need to clean or replace damaged grate clips.
In accordance with the present invention, there is provided a grate clip for a traveling stoker grate. comprising a centrally located supporting boss for operatively connecting the clip to a supporting member of the stoker grate, a generally planar fuel-supporting portion along an upper surface thereof, and a slope-sided lower surface, wherein the sloped-sided lower surface is generally free of surfaces that are parallel to the planar fuel-supporting portion along the upper surface.
In accordance with another aspect of the present invention, there is provided a grate clip for a traveling stoker grate, comprising a first elongated flange piece having a generally planar fuel-supporting portion along an upper surface thereof and a slope-sided lower surface and a threaded opening in the body parallel to the fuel supporting surface, wherein the sloped-sided lower surface is generally free of surfaces that are parallel to the planar fuel-supporting portion, a second elongated flange piece having a body with an upper fuel supporting surface, coplanar with the fuel supporting surface of the first piece when the clip is assembled and a slope-sided lower surface, wherein the sloped-sided lower surface is generally free of surfaces that are parallel to the planar fuel-supporting portion, a bore extending through the body of the second piece parallel to the fuel supporting surface and aligned with the threaded opening when the clip is assembled, the first piece having a transverse notch and the second piece having a transverse notch forming a T-shaped transverse notch when the clip is assembled, and a fastener extending through the bore and into the threaded opening parallel to the fuel supporting surface.
In accordance with yet another aspect of the present invention, there is provided a traveling stoker grate, comprising a plurality of grate clips, and a transport assembly, operatively associated with said grate clips, for moving said grate clips in a continuous loop, wherein at least one of said plurality of grate clips includes a centrally located supporting boss for operatively connecting the clip to the transport assembly, a generally planar fuel-supporting portion along an upper surface thereof, and a slope-sided lower surface, wherein the sloped-sided lower surface is generally free of surfaces that are parallel to the planar fuel-supporting portion along the upper surface.
One aspect of the invention is based on the discovery that the reduction or elimination of horizontal surfaces on the underside of the grate clips reduces the locations in which debris, fuel and molten materials collect and/or solidify. This discovery avoids problems that arise in continuous stoker grates, where a return loop of the grate clips or keys passes beneath an upper plane that supports fuel for combustion. This aspect of the invention can be implemented, for example, by providing a continuously sloped surface on the majority of the underside of the grate clips, thereby shedding the materials that fall or drip through the top of the grate stoker.
The technique described above is advantageous because it is easily applied to the casting or molding techniques for new or replacement grate clips. Moreover, the improved design does not change the functionality of the clip or significantly alter the amount of material used to manufacture it. Hence, the improved design is inexpensive in terms of overall cost when compared to other approaches used to clean the grate stoker, and will likely improve the life of the grate clips and stoker equipment.